Wireless communication devices often require multi-band antennas for transmitting and receiving radio communication signals often called Radio Frequency (RF) signals. For example, network operators provide services on a GSM system in a 900 MHz frequency band typically used in Asia also use a DCS system in a 1800 MHz frequency band typically used in Europe. Accordingly, GSM wireless communication devices, such as cellular radio telephones, should have dual band antennas to be able to effectively communicate at least at both of these frequencies. Also, in certain countries service providers operate on 850 MHz or 1900 MHz frequency bands. Accordingly, GSM wireless communication devices, such as cellular radio telephones, should have multi band antennas to be able to effectively communicate on more than one of these frequency bands.
Current consumer requirements are for compact wireless communication devices that typically have an internal antenna instead of an antenna stub that is visible to the user. Small cellular telephones now require a miniaturized antenna comprising an antenna radiator structure coupled to a ground plane, the ground planes being typically formed on or in a circuit board of the telephone. Further, the antenna radiator structure is installed inside the phone where congested conductive and “lossy” components are placed nearby. The antenna must be able to cover multiple frequency bands to, for instance, accommodate the 900 MHz and 1800 Mhz bands whilst being compact.
Internal antenna radiator structures, such as a Planar Inverted F Antenna (PIFA) or Planar Inverted L Antenna (PILA), that use a radiator element in the form of a micro-strip internal patch antenna, are considered advantageous in several ways because of their compact lightweight structure, which is relatively easy to fabricate and produce with precise printed circuit techniques capable of integration on printed circuit boards.
Internal antenna radiator elements (patch antennas) are typically spaced from circuit board and when viewed in plan view at least most of a surface area of the antenna radiator element overlaps a surface of the circuit board forming a sandwiched region. This sandwich region is filled with one or more dielectric mediums including air and the mount (typically made of plastics) for the radiator element. The antenna's characteristics and performance may be affected by ground planes and signal lines on or in the circuit board that also overlap the antenna radiator element. Also, most known internal patch antennas tend to have a narrow bandwidth, unless their radiator element is sufficiently spaced from the ground plane. One solution to reduce the affects of ground planes, signal lines and also improve the antenna's bandwidth characteristics is to space the antenna radiator element further away from the circuit board. However, this would inevitably result in a thicker device that may not be acceptable for portable communications devices that are tending to become smaller due to consumer requirements. Accordingly, a need exists for relatively compact internal antenna radiator assembly or structure.